This application is for funds to supplemet Grant No. 1RO1NS12045. The purpose of the supplement is to offset project operating expenses (salaries, computer maintenance, subject costs, etc.) which, because of a necessary change in the budget, cannot be covered by the parent grant. The aim of the research has not been changed. It is to explore the possibilities and limitations of a new approach to pitch perception, based on a kind of auditory spectral pattern-recognition. However, because of the progress we have made on the project since the original application was submitted, we are now able to refine the project objectives and extend the range and number of proposed experiments. Several types of experiments are proposed. First, we plan stimulation experiments, in order both to refine the predictions of our model of pitch perception and to extend it to predict actual pitch matching behavior. Second, we propose a series of phychophysical masking experiments designed to measure the important features of the internal spectral representations of certain acoustic stimuli. The masking pattern produced by a stimulus is assumed to be a direct reflection of the internal representation of the power-spectrum of the stimulus. Third, a series of pitch-matching experiments is suggested, to deal with some of the unanswered questions about the effects on pitch of changes in certain stimulus parameters (e.g., relative component amplitude.) Finally, musical interval-recognition experiments are proposed (among others) in order to develop objective measures of pitch strength. Numerical predictions of pitch strength constitute a novel feature of our approach; to our knowledge this represents the first attempt to deal with this attribute of pitch. A few additional experiments are proposed to explore certain features of pitch perception in the hearing-impaired. Specifically, we will consider the problems of diplacusis and the central mediation of pitch in hearing-impaired listeners.